From: "Kismet" <kismet-AT-bigpond.net.au>
To: <puptcrit-AT-lists.driftline.org>
Date: Sun, 30 Apr 2006 19:49:13 +1000
Subject: Re: [Puptcrit] OT-Old Fashionned tool Advice?


As Ray pointed out its not a process to be be undertaken lightly and 
probable not worth it for a fine file...all my bastards are done for stone 
work but its funny how familiarity breeds contempt, having being taught the 
process some cough cough splutter cough years ago I resort to it 
occasionally for a finish on a sculpture or a part for one of my 
bus/motorcycle/vintage car/sculpture tool collection...never needed it for a 
puppet though.....and have never encountered a suggestion that it may be 
unsafe... beyond the fact that we are dealing with very hot metals
The processes are the same.... Case hardening, in the case of mild (low 
carbon) steel involves heating a metal to a temperature that allows 
additional carbon to combine with the iron molecules to form a harder steel 
on the outer mico millimetres, forming a case.(High carbon steels only 
require heating and then quick steady cooling)  there are proprietory 
"glazes" that can be applied at a lower temperature and then heating to a 
higher temperature to allow the carbon to impregnate the steel, in this case 
the item is plunged into cool water WITH oil floating on top to reduce the 
risk of thermal shock. In my example the  high carbon content liquid, motor 
oil, impregnates the steel with carbon as it cools. The problem with rapid 
cooling, such as using water, is the crystalising effect on the steel 
molecules wich CAN create a thermal shock, oil cools a lot slower (in 
relative terms) and creates stronger molecular bonds.....I think Im 
remembering my physics right, been a long time. Apart from an occasional 
flare from an overheated piece Ive never heard of any one encountering a 
problem and its certainly no more dangerous than what a deep fryer 
encounters at McDonalds every day.
These days a lot of case hardening is actually replaced by using a MIG 
welder to create a basket around an item, something to mention at a 
party...or you could mention that early case hardening was done by cramming 
the mild steel item into a sealed tin with cow bones and hair then heating 
it to glowing red hot for a few hours. The smouldering bones and hair, 
without much oxygen, created a carbon gas that impregnated the steel....... 
Obviously I go to some great parties!

D.
Dont know much about Stainless except that you cant cut it very well with an 
Oxy or a grinder which means its not much use to me. 

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